The invention relates broadly to structures which will absorb the impact energy of a moving object. More particularly, the invention is directed to use of ceramic foams or glass foams, as energy absorbing materials, to cover rigid members, such as highway structures.
It is common practice to use plastic resin foams, such as the closed-cell polyurethanes, polystyrenes, and polyethylenes, as cushioning materials. For example, these plastic foams are frequently used as energy absorbers to prevent damage to objects during shipping. Another use of this material is as crash padding in automobiles to prevent harm to the occupants of the vehicle during a collision. The plastic foams, however, are not entirely satisfactory as energy absorbing materials.
A particular problem is that when an object impacts with a plastic foam, there is a distinct recoil or rebound of the object. The recoil is caused by trapped gas in the cell structure of the foam. In other words, if the cell walls do not fracture upon impact of the object with the plastic foam, the trapped gas will compress. When the impact pressure is released, therefore, the gas expands the cell walls and pushes back on the impacting object.